If you are really above 7k Rpm in every gear and still want more power then a stronger motor is a good option.
You could always try to shave as much wight of the bike as possible.
Aftermarket muffler will be 3-5kg lighter. Remove the rear trellis frame (it does
affect structure of the bike, but it depends on your use of the bike) and grab handles.
Aftermarket aluminum handlebars. Stock bars are very heavy.
Use OEM wind screen instead of big aftermarket ones.
Theoretically, if you change the headlight bulbs to HID and posi-lights to LED less power will be wasted on making electricity.
If you can afford it, consider replacing the wheels with lighter ones from sport bikes.
Consider new suspension all around or at least new springs for a maximum feedback.
Good brakes will
make you go faster.
What I consider most important: spend big money on a sticky race tires. Corner speed and grip is where the fun is and good tires will give you this.
I never seen a report about an aftermarket air filter making a difference for the Versys. On the contrary.
Go to the dealer and trade in your Versys for a Versys1000 or KTM SMT and hold on to your pants.